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• ffmpeg change framerate : Question about bitrate [closed]

  9 février, par schweigerson

  Thanks to the forum, I successfully can reduce the frame rate of a video.

  


  ffmpeg -i input_50fps.mp4 -filter:v fps=25 output_25fps.mp4

  


  Input and output have a similar bitrate as well as filzesize :

  


  




  


  


  


  


  


  



  


  


  


  


  


  


  


  


  


  


  File	bitrate	filesize
  input_50fps.mp4	2900kBit/s	1.9GB
  output_25fps.mp4	2528kBit/s	1.7GB

  


  Assumption : Divide the number of frames into half should both reduce the bitrate and the filesize accordingly (half the size).

  


  Question : Does it make sense to enforce the reduction of the bitrate to approx. half the original one, when I reduce the framerate by to 50% (e.g. with -b:v 1500k) ? IMHO, the video quality should be comparable to the original video then.

  


  Note : I may make according test runs, but I perhaps do not have the ability to recognize the quality difference as I'm not an advanced video expert.

  


  Would be happy to read your advice.

  


• Comparing the video/audio output of ffmpeg commands between versions to test for regessions

  4 février, par lavantgarde

  Our software uses ffmpeg to do various video/audio encoding (e.g. changing volume, re-encoding to a different video format (e.g. yuv420p), scaling, etc.)

  


  Every few months we upgrade ffmpeg versions, and we've found that sometimes parameters change and regressions are introduced.

  


  What ffmpeg tools could we use to create unit tests to validate certain commands for regressions ?

  


  I believe checking hashes won't be enough ; doing visual inspections manually is also something we'd like to avoid to automate.

  


  Here's an example pseudocode :

  


  var ffmpegV1 = "C:\ffmpegv1.exe";
var ffmpegV2 = "C:\ffmpegv2.exe";

var inputVideo = "C:\video.mp4";

var outputVideoV1 = "C:\OutputV1.mp4";
var outputVideoV2 = "C:\OutputV2.mp4";


ffmpegV1.Encode($"-y -i {inputVideo} -ar 22050 -ab 64k -ac 1 -s 120x40 -crf 30 -g 150 OutputV1.mp4");


ffmpegV1.Encode($"-y -i {inputVideo} -ar 22050 -ab 64k -ac 1 -s 120x40 -crf 30 -g 150 OutputV2.mp4");



// This is where I want to figure out how I can programmatically determine that the videos are the same, or within some tolerance of difference, e.g.

bool isAudioTheSame = FfmpegTest.CompareAudio(outputVideoV1, outputVideoV2, Epsilon.Tolerance);

bool isVideoTheSame = FfmpegTest.CompareVideo(outputVideoV1, outputVideoV2, Epsilon.Tolerance);



  


  I'm not a video/audio expert, so I'm not really sure how to flesh these out. Do I just compare the bytes ? Or is there another ffmpeg tool/command to use ?

  


• How to improve Desktop capture performance and quality with ffmpeg [closed]

  6 novembre 2024, par Francesco Bramato

  I'm developing a game capture feature from my Electron app. I'm working on this since a while and tried a lot of different parameters combinations, now i'm running out of ideas :)

  


  I've read tons of ffmpeg documentation, SO posts, other sites, but i'm not really a ffmpeg expert or video editing pro.

  


  This is how it works now :

  


  The app spawn an ffmpeg command based on user's settings :

  


  

  • Output format (mp4, mkv, avi)

  


  • Framerate (12, 24, 30, 60)

  


  • Codec (X264, NVidia NVENC, AMD AMF)

  


  • Bitrate (from 1000 to 10000kpbs)

  


  • Presets (for X264)

  


  • Audio output (a dshow device like StereoMix or VB-Cable) and Audio input (a dshow device like the Microphone)

  


  • Final Resolution (720p, 1080p, 2K, Original Size)

  


  


  The command executed, as far, is :

  


  ffmpeg.exe -nostats -hide_banner -hwaccel cuda -hwaccel_output_format cuda -f gdigrab -draw_mouse 0 -framerate 60 -offset_x 0 -offset_y 0 -video_size 2560x1440 -i desktop -f dshow -i audio=@device_cm_{33D9A762-90C8-11D0-BD43-00A0C911CE86}\wave_{D61FA53D-FA37-4BE7-BE2F-4005F94790BB} -ar 44100 -colorspace bt709 -color_trc bt709 -color_primaries bt709 -c:v h264_nvenc -b:v 6000k -preset slow -rc cbr -profile:v high -g 60 -acodec aac -maxrate 6000k -bufsize 12000k -pix_fmt yuv420p -f mpegts -


  


  one of the settings is the recording mode : full game session or replay buffer.
In case of full game session, the output is a file, for replay buffer is stdout.

  


  The output format is mpegts because, as far i have read in a lot of places, the video stream can be cut in any moment.

  


  Replays are cutted with different past and future duration based on game events.

  


  In full game session, the replays are cutted directly from the mpegts.

  


  In replay buffer mode, the ffmpeg stdout is redirect to the app that record the buffer (1 or 2 minutes), when the replay must be created, the app saves on the disk the buffer section according to past and future duration and with another ffmpeg command, copy it to a mp4 or mkv final file.

  


  Generally speaking, this works reliably.

  


  There are few issues :

  


  

  • nonetheless i ask ffmpeg to capture at 60fps, the final result is at 30fps (using -r 60 will speed up the final result)

  


  • some user has reported FPS drops in-game, specially when using NVidia NVENC (and having a NVIDIA GPU), using X264 seems save some FPS

  


  • colors are strange compared to original, what i see on screen, they seem washed out - i could have solved this using -colorspace bt709 -color_trc bt709 -color_primaries bt709 but don't know if is the right choice

  


  • NVIDIA NVenc with any other preset that is not slow creates videos terribly laggy

  


  


  here two examples, 60 FPS, NVIDIA NVENC (slow, 6000kbs, MP4

  


  Recorded by my app : https://www.youtube.com/watch?v=Msm62IwHdlk

  


  Recorded by OB with nearly same settings : https://youtu.be/WuHoLh26W7E

  


  Hope someone can help me

  


  Thanks !